Fumiyoshi Kirino, Shigekazu Ohotomo and Nagatsugu Koiso
Central Research Laboratory Hitachi, Ltd., 1-280 Higashi-koigakubo Kokubunji-shi, Tokyo 185 Japan
Dependences of corrosion resistance of an Al-doped Fe-Ta-C magnetic thin film on Al, Ta, and C contents were examined. The higher the concentration of the doped Al in Fe-Ta-C alloy, the higher became the pitting potential and the oxidation potential. The resistance against corrosion such as pitting corrosion and wet corrosion increases with increasing Al concentraition. When the Al content in the Fe-Ta-C film is incresed to 9.8 at%, a passive film is formed on the alloy film surface where the pitting potential is 0.5 V (vs. Ag/AgCl electrode), and oxidation of the metal such as Fe does not occur. This film is thus highly resistant to corrosion when it is immersed in 0.5N-NaCl solution. The corrosion resistance depends on [Ta]/[C] ratio. When the [Ta]/[C] ratio is greater than 0.72, the film with 9.8 at%Al corrodes in 0.5N-NaCl solution. When the [Ta]/[C] ratio is between 0.52 and 0.68, the highest corrosion resistance is realized. The crystal structure analysis using X-ray diffraction indicates that the grain size of TaC precipitates is very small in these films. Magnetic properties of the 9.8 at%Al-doped Fe-Ta-C film (Bs=1.3 T, Hc=20 A/m, μ=3000, and λs=2{×}10-6) are suitable for magnetic head applications.
(Received July 10, 1996)
corrosion resistance, pitting corrosion, iron-tantalium-carbon alloy, passive film, the magnetic head, the magnetic properties, tantalium/carbon ratio, pitting potential
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